1. Field of the Invention
The present invention relates generally to walls and building foundations and, more particularly, to a wall having a cantilevered section and a foundation unit incorporating such a wall for supporting a building.
2. Description of the Prior Art
Conventional building foundations include a floor section disposed on the horizontal surface of an excavation and vertical sidewalls adjoining the floor section supported by footers formed in the excavation. Although such conventional foundations are suitable for supporting a building constructed on a horizontal surface, there are several disadvantages associated with using such a foundation to support a building on a hillside. The uphill-vertical wall must resist the force exerted on the foundation by the hillside uphill from the foundation. Accordingly, the uphill-vertical wall must be thicker than it would have to be to support only the building constructed on the foundation. Moreover, the large force exerted by the hillside on the uphill-vertical wall makes it advantageous to minimize the size of the portion of the building located beneath the surface, thereby maximizing the size of the portion of the building exposed to the elements and in turn, the amount of exterior finishing materials needed to construct the building.
In underwater construction, it is known that a slight incline of the retaining wall portion of a foundation unit will help to distribute the multi-directional forces exerted against the unit. Judson U.S. Pat. No. 921,545 which issued on May 11, 1909 discloses a caisson for use in foundations in water. The caisson shown and described by the Judson patent is a box-like receptacle having a rear wall, a front wall and two opposing side walls. The side walls, shown only in a top plan view of the caisson, are not described. The rear wall is inclined slightly from the vertical and the front wall preferably lies in a plane parallel to the rear wall.
The structure described by the Judson patent is particularly adapted for use under water. The rear wall acts as a retaining wall. The material retained exerts a generally horizontal force in one direction against the rear wall. The water, which exerts a generally horizontal force in the opposite direction against the front wall, resists the opposing force of the retained material. A cap which is positioned over the caisson when it is in place, exerts a downward force.
The caisson is designed to permit it to be floated to the desired location. It is then filled with heavy material and capped for use. The heavy filling and the slight backwards incline of the rear wall help to evenly distribute the multi-directional forces exerted against the caisson by shifting the center of gravity rearwardly from the foot of the front wall. To accommodate the floatation requirement, the incline of the rear wall cannot be too great, thus the center of gravity cannot be shifted too far to the rear.
In hillside construction, the force exerted by the hillside is not resisted in part by an opposing force exerted by water. In addition, the downward force or weight bearing against the walls of a foundation by a building is greater than the force of the cap on the walls of the caisson in the Judson patent. In other words, a building weighs more than the cap. Thus, the requirements for the distribution of forces to provide a stable foundation are markedly different for land based construction. The foundation unit must itself resist the generally horizontal forces of the hillside and the downward force, or weight, of the building constructed on the foundation. The strength of the those forces, of course, varies depending upon the local soil conditions and the design of the building. Furthermore, because it is desirable to be able to use the space defined by the foundation, it is undesirable to fill that space with heavy material to stabilize the foundation. Anchors or piles have been used in some structures for stability.
Another problem too often associated with hillside construction is the failure of an older, existing foundation under a building or the subsidence of the ground support. To prevent damage to the building, the old foundation must be repaired or the subsidence corrected. Meanwhile, a temporary underpinning, usually beams--positioned under the building must be installed. When the soil under the beam is not stable, however, or when the building is constructed on or near the top edge of a hillside it is difficult to effectively place the underpinning. Furthermore, it may not be possible to correct the old foundation of the subsidence. There is a need, therefore, for a permanent underpinning for a building which can be used when conventional means of correction are not effective.
It is an object of the present invention to provide a foundation unit for land based construction that reduces the force exerted by a hillside. It is a further object of the present invention to provide a foundation that evenly distributes the forces exerted against it to provide a stable structure. It is another object of the present invention to provide a foundation which will increase the available living space of the building. Finally, it is an object of the present invention to provide a component of the foundation which can be used for underpinning an existing building when either lateral ground support erodes or the existing, older foundation fails.